1. Field of the Invention
The present invention provides a process for recovering alkanolamines. More specifically, the present invention is an improved process for converting an oxazolidone such as hydroxypropyloxazolidone (HPOZD; [3-(2-hydroxypropyl)-5-methyl-2-oxazolidinone]) to di-isopropanolamine (DIPA).
2. Description of Related Art
In the processing of gas and liquid streams, acid gas impurities (typically hydrogen sulfide and carbon dioxide) are removed by contact with an alkanolamine solution containing an alkanolamines such as DIPA. Alkanolamine solutions are used because of their relatively high absorption capacity of acid gases, and the relative ease with which acid gases can be stripped from the amine-containing solution.
One such process yields HPOZD, an impurity reaction product of the DIPA and carbon dioxide (CO2). The reaction forming the HPOZD molecule occurs with the simultaneous dehydration of one water molecule (H2O) from the DIPA molecule. Other such processes yield analogous oxazolidones using other alkanolamines.
An existing process for converting this impurity (the HPOZD) requires several lengthy stepwise heating and processing cycles at dilute caustic (with corresponding cation) concentrations. This process is tailored to convert the oxazolidone back to DIPA, releasing CO2 into the amine solution to form carbonates and/or bicarbonates, subsequently removing the majority of the cations from the entire reaction solution using ion exchange resins. Because of the concern of the capacity to remove cations from the reaction solution, the concentration of the caustic reactant is kept low, resulting in a process that has a typical HPOZD to DIPA conversion efficiency of about 20% to 25% per reaction process step. The entire reaction mixture including all cations from the added caustic is processed through the ion exchange resins. The overall process including rinsing and regenerating the cation exchange resins adds considerable amounts of water to the amine-containing solution which must be removed by a distillation procedure.
This existing process treats a quantity of an amine-containing solution obtained from an acid gas stripper column used for acid gas removal. The amine-containing solution may be composed of an alkanolamine such as DIPA, a physical solvent such as tetramethylene sulfone, water, CO2 and the degradation product identified as HPOZD. This solution is treated with a dilute caustic solution, such as but not limited to potassium hydroxide (KOH), at elevated temperatures at atmospheric pressure to hydrolyze (add one molecule of H2O) to the HPOZD molecule and simultaneously cleave the CO2 molecule out of the HPOZD molecule, resulting in the production of free DIPA as well as carbonates and/or bicarbonates. The DIPA generated by this process is a benefit to the user in that it is a primary active ingredient of the amine-containing solution used for acid gas removal. The reduction of the HPOZD content of the amine-containing solution used for acid gas removal by this process is a benefit in that the HPOZD decreases the efficiency of the amine-containing solution to perform its function of scrubbing acid gas from gas and/or liquid process streams.
After processing the amine solution through the cation exchange resins, it is returned as “clean amine” to the amine circulation system where excess water and CO2 (from carbonates and/or bicarbonates) are stripped from the solution.